blog = post based structure
website = page based structure
A blog is a website and any WordPress blog can be restructured from being post based to being page based. You can use any theme here at WordPress.com to create a page based structure ie. a website rather than a post based structure ie. a blog. http://wordpress.com/themes/
1. You can create a static front page and a page for posts.
Please be sure you fully understand the differences between Pages and Posts. http://en.support.wordpress.com/post-vs-page/
The front page of the blog by default will display your posts (not pages) in reverse chronological order, with the most recently published post on top. If you do not want all the posts to show on the front page, then you can create a static front page called for example “Welcome” for your site and a “Blog” page for posts.
To do that create two pages > http://en.support.wordpress.com/pages/ After you do that you go to > Settings > Reading and make the designation change and click “save changes”.
2. Most but not all themes have a top horizontal menu bar. This is where tabs to static pages are displayed. However, if we want to we can create a cusom menu and display links to other items. http://en.support.wordpress.com/pages/
3. There are themes with either right hand or left hand sidebars and some have both. Many themes provide the ability to select a page template that hides the sidebar(s).
4. The majority of themes have custom header and custom background features. Some have featured images in featured posts.
On the bottom of your Admin page you will find a link to the Learn WordPress.com blogging Tutorial prepared by Staff. http://learn.wordpress.com/
The support documentation is all found at the Support link http://en.support.wordpress.com which is also on the bottom of your Admin page.